92 CHEMICAL ENGINEERING K = Constant = 1.43 to 1.65—average, 1.5, w2 = Width of belt in inches squared, V = Speed of conveyor in feet per minute, >w' = Weight of material handling in pounds per cubic foot. Power Requirements.—The consumption of power by belt conveyors depends somewhat upon the method of their lubrication, but is so low that the power requirements for well grease-lubricated equipment may be taken as the standard and reduced by an arbitrary amount to be approximately accurate for equipment mounted on ball or roller bearings. Formula (8) gives the power requirements for a grease-lubricated conveyor well aligned and properly cared for. (0.00009™2 V + 0.08PF)L -f WH „ . ,0, Horsepower =-------------------^------------------Formula (8) Where, w — Width of conveyor belt in inches, V — Speed of conveyor in feet per minute, W - Load handled in tons per hour, L = Total length of conveyor in feet, and H = Rise in length of conveyor in feet. Horsepower additional required for each tripper or fixed dump = 1 hp. for each incli of belt width in excess of 10 in. For ball- or roller-bearing conveyors reduce power requirements on horizontal stretches by 33^ per cent. The costs of belt conveyors and of conveyors and elevators in general are so susceptible to the market prices for materials and to manufacturing costs that exact figures cannot well be presented, but relative costs can be arrived at which will enable accurate estimates of market prices to be arrived at by comparison and which will serve as reliable guides for ascertaining the relative economy of various types of conveyors and elevators. This method of presenting costs will be adhered to for all types of conveyors and elevators discussed, the relative costs established on a common base so as to be mutually comparable. Formula (9) gives the relative cost of high-grade belt conveyors fully equipped with durable rubber belt and all accessories; Formulas (9a), (96) and (9c), the relative costs of discharging devices; while Formula (10) gives an equation for ascertaining the annual depreciation—expressed in the same relative units—to be anticipated with proper care and attention to the equipment. RCbc = (QA5w - 1.7)L -f 3.65w? Formula (9) RCfd =2*0 + 12 • Formula (9a) RChi = 6.3w + 75 + Q.SILt Formula (96) RCat = llw + 132.5 + 0.81L, Formula (9c) RDbc = (0.08w - 0.32)L + 0.365w Formula (10) Where, RCbc = Average relative cost of belt conveyors, RCfd = Average relative cost of fixed dumps, RCht - Average relative cost of hand propelled trippers, RCat = Average relative cost of automatic trippers, RDic — Average relative depreciation—annual, w - Width of conveyor belt in inches, L = Total length of conveyor in feet, and Lt = Lengthtripper travel in feet.